This invention relates generally to adhesives, particularly adhesives that are useful on fluorine-containing or polycarbonate surfaces and, more specifically, to pressure sensitive adhesives that include a copolymer of one or more alkyl (meth)acrylate monomers, one or more amide-functional monomers, and optionally one or more acidic monomers.
Graphic marking films or labels that include vinyl films coated with acrylic pressure sensitive adhesives (PSAs) are well-known in the art. Such films are typically applied to plasticized polyvinylchloride substrates which may have a thin dirt- and chemical-resistant top coating. Such clear top coatings include fluorine-containing polymers, for example. One such product includes a clear top surface containing a blend of polymethylmethacrylate (PMMA) and a copolymer of vinylidenefluoride (VDF) and chlorotrifluoroethylene (CTFE). Typically, the higher the fluoropolymer content of such surfaces, the better the dirt repellancy. As long as this clear top surface includes a major amount of PMMA, adequate bond formation of a vinyl marking film is obtained using an acrylic PSA containing a copolymer of an alkylacrylate and acrylic acid (AA). This adhesive, however, does not work effectively on clear top surfaces that include a major amount of fluorine-containing polymer and a minor amount of PMMA or no PMMA. In general, the ability to provide such label and graphic marking films, or other articles, with high bonding strength to surfaces containing fluorine has not been generally possible without surface treatment of the substrate (e.g., chemical priming).
Similarly, it is difficult to adhere articles to substrate surfaces that include polycarbonates, or plasticized polymers such as polyvinylchloride.
There are a limited number of known adhesives, many of which are based on acrylate chemistry, that can be used, however. For example, U.S. Pat. No. 5,612,136 (Everaerts et al.) discloses acrylate-based (i.e., acrylic) pressure sensitive adhesive compositions that adhere well to acidic surfaces. The adhesive is prepared from an alkyl acrylate, wherein the alkyl group includes four or more carbon atoms, which is copolymerized with basic monomers, such as dialkyl substituted amides. Lower (less than C4) alkyl acrylates can be copolymerized with such monomers provided that the glass transition temperature (Tg) of the resultant polymer is below about xe2x88x9220xc2x0 C. U.S. Pat. No. 5,905,099 (Everaerts et al.) discloses heat-activatable adhesive compositions prepared from a low Tg (homopolymer Tg of no greater than about 0xc2x0 C.) alkyl acrylate, wherein the alkyl group includes two or more carbon atoms, a high Tg acrylate (homopolymer Tg of at least about 50xc2x0 C.), such as a cycloalkyl or aromatic acrylate, and a polar functional monomer such as a carboxylic acid, an N-substituted amide, an N-substituted amine, and a carbamate. Weakly basic monomers, such as N,N-dimethyl acrylamide and N-vinyl pyrrolidone are disclosed as enhancing adhesion to plasticized and rigid polyvinylchloride. Acidic functional monomers, such as acrylic acid, are disclosed as enhancing adhesion to polar surfaces such as glass, metals, paint, and basic surfaces.
U.S. Pat. No. 4,985,488 (Landin) discloses a plasticizer-resistant acrylate-based adhesive prepared from nitrogen-containing alkyl acrylate monomers, wherein the alkyl group includes four or more carbon atoms. U.S. Pat. No. 5,334,686 (Ando et al.) discloses acrylate-based adhesives prepared from alkyl acrylates, wherein the alkyl group includes four or more carbon atoms, dialkyl-substituted acrylamides, and acids. JP 8-143843 (Nitto) discloses removable acrylate-based adhesives prepared from alkyl acrylates, wherein the alkyl group includes two or more carbon atoms, N,N-dialkyl acrylamides, and carboxylic acids. U.S. Pat. No. 4,605,592 (Paquette et al.) discloses plasticizer-resistant acrylate-based pressure sensitive adhesive compositions prepared from alkyl acrylates, wherein the alkyl group includes four or more carbon atoms, to prevent vinyl decorative graphics from wrinkling. JP 06-108025A (Nippon) discloses acrylate-based adhesives for bonding cellulose to glass without appearance defects. One example includes a copolymer of, for example, n-butyl acrylate, methyl acrylate, acrylic acid, and an amide such as N,N-dimethyl acrylamide, wherein the amide monomer is present in an amount of 0.3-10 weight percent of the copolymer.
There is still a need in the art for other adhesives that can be used to adhere articles to surfaces such as fluorine-containing or polycarbonate surfaces that do not typically demonstrate particularly good adhesion.
This invention relates generally to adhesives useful for adhering articles to fluorine-containing or polycarbonate surfaces, for example. Preferably, adhesives of the present invention have an initial level of adhesion that allows an article to be removable and/or repositionable, but which builds to a greater level of permanency with time, heat, and/or pressure, for example. The adhesive may be pressure sensitive or heat activatable.
In one embodiment, a pressure sensitive adhesive (PSA) having a Tg of at least about xe2x88x9220xc2x0 C. is provided. The PSA includes a copolymer comprising: at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbons on average; at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbons on average; and greater than 10 parts by weight, based on the total weight of monomers, of at least one copolymerized monoethylenically unsaturated monomer having a secondary or tertiary amide group of the formula xe2x80x94C(O)NR1R2 wherein R1 and R2 are each independently H or a saturated or unsaturated hydrocarbon moiety, which optionally forms a ring with the carbonyl carbon (xe2x80x94C(O)) of the amide group.
In another embodiment, the present invention provides an adhesive (which can be a pressure sensitive or heat activatable adhesive) having a Tg of at least about xe2x88x9220xc2x0 C. that includes a copolymer comprising: at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbons on average; at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbons on average; and greater than 10 parts by weight, based on the total weight of monomers, of at least one copolymerized monoethylenically unsaturated monomer having a secondary or tertiary amide group of the formula xe2x80x94C(O)NR1R2 wherein R1 and R2 are each independently H or a saturated or unsaturated hydrocarbon moiety, which optionally forms a ring with the carbonyl carbon (xe2x80x94C(O)) of the amide group. In this embodiment, all of the copolymerized monoethylenically unsaturated (meth)acrylic acid esters of the copolymer have a Tg of less than about 50xc2x0 C. as a homopolymer. Preferably, the copolymer further includes at least one copolymerized acidic monomer.
Preferably, a 50-micron thick polymeric plasticized vinyl film having a 35-micron thick layer of the adhesive disposed thereon has a 180xc2x0 peel adhesion value of no greater than about 35 N/100 mm, measured at a 30.5 cm per minute peel rate, from a surface comprising an 80/20 polyvinylidenefluoride/polymethylmethacrylate blend after contact for 24 hours at 22xc2x0 C. Preferably, if stored for 7 days at 66xc2x0 C., the 80xc2x0 peel adhesion value is at least about 70 N/100 mm.
In yet another embodiment, the present invention provides a pressure sensitive adhesive having a Tg of at least about xe2x88x9220xc2x0 C. The PSA includes a copolymer comprising: at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbons on average and which as a homopolymer has a Tg of less than about 0xc2x0 C.; at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbons on average and which as a homopolymer has a Tg of less than about 50xc2x0 C.; and greater than 10 parts by weight, based on the total weight of monomers, at least one copolymerized monoethylenically unsaturated monomer having a secondary or tertiary amide group of the formula xe2x80x94C(O)NR1R2 wherein R1 and R2 are each independently H or a saturated or unsaturated hydrocarbon moiety, which optionally forms a ring with the carbonyl carbon (xe2x80x94C(O)) of the amide group; wherein a 50-micron thick polymeric plasticized vinyl film having a 35-micron thick layer of the pressure sensitive adhesive disposed thereon has a 180xc2x0 peel adhesion value of no greater than about 35 N/100 mm, measured at a 30.5 cm per minute peel rate, from a surface comprising an 80/20 polyvinylidenefluoride/polymethylmethacrylate blend after contact for 24 hours at 22xc2x0 C., and after 7 days at 66xc2x0 C. has a 180xc2x0 peel adhesion value of at least about 70 N/100 mm, measured at a 30.5 cm per minute peel rate.
The present invention also provides an article comprising a substrate surface comprising a nonperfluorinated fluoropolymer derived from at least one hydrofluoro monomer, and an adhesive-coated article adhered thereto, and a method of adhering. The adhesive-coated article comprises a backing (e.g., a film or a foam), which has disposed on at least one major surface thereof an adhesive which is adhered to the substrate surface; wherein the adhesive comprises a copolymer comprising at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester (preferably, at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbon atoms on average, and at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbon atoms on average) and at least one copolymerized monoethylenically unsaturated monomer having a secondary or tertiary amide group. Preferably, the substrate surface further includes a polymethylmethacrylate blended with the nonperfluorinated fluoropolymer derived from at least one hydrofluoro monomer. In certain embodiments the copolymer further includes at least one copolymerized acidic monomer.
A further embodiment of the present invention is an article comprising a substrate surface comprising a polycarbonate and an adhesive-coated article adhered thereto, and a method of adhering. The adhesive-coated article comprises a backing (e.g., a film or a foam), which has disposed on at least one major surface thereof an adhesive which is adhered to the substrate surface; wherein the adhesive comprises a copolymer comprising: at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester (preferably, at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbon atoms on average, and at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbon atoms on average); and at least one copolymerized monoethylenically unsaturated monomer having a secondary or tertiary amide group of the formula xe2x80x94C(O)NR1R2 wherein R1 and R2 are each independently H or a saturated or unsaturated hydrocarbon moiety, which optionally forms a ring with the carbonyl carbon (xe2x80x94C(O)) of the amide group. In certain embodiments the copolymer further includes at least one copolymerized acidic monomer.
A still further embodiment of the present invention is an article comprising a substrate surface comprising a plasticized polymer and an adhesive-coated article adhered thereto, and a method of adhering. The adhesive-coated article comprises a backing (e.g., a film or a foam), which has disposed on at least one major surface thereof an adhesive which is adhered to the substrate surface; wherein the adhesive has a Tg of at least about xe2x88x9220xc2x0 C. and comprises a copolymer comprising: at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having less than 4 carbon atoms on average; at least one copolymerized monoethylenically unsaturated (meth)acrylic acid ester comprising an alkyl group having at least 4 carbon atoms on average; at least one copolymerized monoethylenically unsaturated monomer having a secondary or tertiary amide group; and at least one acidic monomer. In this embodiment, all of the copolymerized monoethylenically unsaturated (meth)acrylic acid esters of the copolymer have a Tg of less than about 50xc2x0 C. as a homopolymer.
Methods of adhering an article to a substrate surface are also provided.